This invention relates to a photosensitive composition, and more particularly to a photoresist with a high resolution suitable for fabrication of semiconductor devices.
For improving the performance of semiconductor devices such as IC, LSI, etc., finer processings are necessary, and thus a particularly higher resolution is required for the photoresist for use in the processing.
Photoresists can be classified into two groups, i.e. a positive type which becomes soluble in solvents by light exposure and a negative type which becomes insoluble in solvents by light exposure. Most of the positive type photoresists for use in the fabrication of semiconductor devices are mixtures of an alkali-soluble phenolic resin as a film-forming constituent with a naphthoquinonediazide derivative as a photo-sensitive constituent. Most of the negative type photoresists for use in the fabrication of semi-conductor devices are mixtures of cyclized rubber with an aromatic bisazide as a photosentive constituent.
Comparison of the resolution of the two groups of photoresists reveals that the positive type photoresist has a higher resolution than the negative type photoresist, and consequently positive type photoresists recently are more often used in the fabrication of high performance semiconductor devices.
The reasons why the positive type photoresist has a higher resolution than the negative type photoresist are that;
(1) the positive type photoresist has a higher contrast than the negative type photoresist, and
(2) the positive type photoresist can be developed without any swelling in a developer, whereas the negative type photoresist swells in a developer and its pattern sometimes may get out of shape or may be deformed.
Even in the case of negative type photoresists, a higher resolution can be expected, if it can have a higher contrast and exhibits no swelling in a developer.
It is known among the photoresists for use in other fields than the fabrication of semiconductor devices that there are negative type photoresist which shows no swelling in a developer. For example, it is well known that a mixture of an alkali-soluble phenolic resin with an aromatic azide is applicable as a negative type photoresist for photolithography, and this photoresist has no swelling phenomenon when developed in an aqueous alkaline solution. Japanese Patent Publication No. 45-22082 discloses a negative type photoresist containing an aromatic azide compound and an alkali-soluble phenol-formaldehyde resin, and Japanese Patent Publication No. 53-34902 discloses a negative type photoresist containing an aromatic azide compound and polymers of hydroxystyrene.
However, no cases have been found, where these photoresists are used in the fabrication of semiconductor devices, because it seems that these photoresists have been developed mainly for the photolithographic application, and are suitable for application as a film having a thickness of several ten microns, and are not always suitable for application as a film having a thickness of from less than one micron to a few microns as in the fabrication of semiconductor devices.